Petroleum Goes To Finishing School

Be forewarned, this article might remind you of chemistry class, and it might get a little technical, but just hold tight, this is stuff that everybody needs to know, so take a seat, read up, and don't worry, we won't test you on this.

You should all know by now that gasoline, diesel, and nearly every other fuel used to power vehicles comes from petroleum, or crude oil. But what many of you out there probably don't know is how that crude oil is transformed into the myriad fuels, lubricants, and plastics that we use every day.

Crude oil is made up of hydrocarbons, which are molecules that are made of hydrogen and carbon. Hydrocarbon molecules can form chains or rings and can vary in length. The properties of hydrocarbons that make them so useful are that they are extremely versatile and they contain a lot of energy. If we put it into terms of food calories, a gallon of gasoline would have as many calories as about 18 gallons of Mountain Dew. That's just gasoline, just how much energy is stored in hydrocarbons depends on the size of the molecule: Larger molecules store more energy. Small hydrocarbon molecules include methane and propane; slightly larger molecules are used to make liquid fuels like gasoline and diesel, while the largest hydrocarbon molecules make up lubricants like motor oil and grease.

The problem is that crude oil contains all of these different lengths of hydrocarbons and must be sorted out before they are used. That's where refineries come in. The oldest method of refining crude oil is fractional distillation. The different hydrocarbon lengths relate directly to their boiling points, shorter molecules have a lower boiling point, and longer molecules won't boil until they reach temperatures approaching 1,100 degrees F. The boiling point is obviously the temperature that the liquid hydrocarbon becomes a vapor, but another way to think about the boiling points is what that means to the vapor when it cools. When a vapor drops below its boiling point as it cools down, it will condense back into a liquid. This property allows refineries to sort hydrocarbons into fractions by heating the crude oil with steam until the various hydrocarbons boil off, causing the hydrocarbon vapors to rise where they cool and condense in distillation towers. Longer hydrocarbon molecules don't have to rise far from the heat source before they condense, so they wind up at the bottom of the distillation towers, while diesel, gasoline, and propane have to move farther away. The newly organized hydrocarbons are called fractions, and 80 years ago, that was as refined as many fuels and oils got, but due to strict emissions standards and performance demands, these fractions need further processing before leaving the refinery.

Newer chemical processes can be used on the fractions to break up or reform hydrocarbon molecules in order to fine-tune the refinery output and maximize profits. Sixty years ago, a 42-gallon barrel of crude oil would yield only 11 gallons of gasoline. Today, the demand for gasoline is much higher. Rather than distilling barrel after barrel of crude oil only to have excess kerosene, diesel, and solvents pile up, refineries use newer methods of treating fractions. Some refineries are able to convert over half of their crude oil into gasoline. This second round of refining breaks up the residual hydrocarbons-the leftovers-into useful products. Pieces are pulled off one and bolted onto another. This second round is where refineries are able to turn a profit, since hydrocarbons that were treated like waste sixty years ago are now being sold.

Gasoline is made up of a blend of hydrocarbons that have a chain of 7 to 11 carbon molecules. Octane is a hydrocarbon with eight carbon atoms that is resistant to igniting under compression. The octane rating of fuel describes how the fuel will resist pre-ignition under compression. Gasoline with an 87 octane rating acts as though it is 87 percent octane and 13 percent heptane. Heptane is a hydrocarbon that has seven carbon molecules and is poor at resisting ignition. If you've ever been to a gas station or track that sold racing gas, you are probably wondering how octane ratings higher than 100 are possible, after all, giving 110 percent is usually only something professional athletes can achieve. To get increased octane ratings, refineries either increase the percentage of octane in the gasoline blend or introduce additives or both. Tetraethyl lead was the additive of choice for decades until the toxic side effects were realized. The musclecar heyday of the late '60s and early '70s owes a lot to cheap, high-octane, leaded fuel that allowed OEMs to equip cars with high-compression engines.

Now that you know how gasoline is made at the refinery, and what octane ratings represent, we need to focus on what the different grades of gasoline mean to you and your truck. The majority of automotive engines are perfectly happy with regular 87-octane fuel. A few high-performance cars-and even fewer trucks-come with recommendations for high-octane fuel. Some people think that the higher-performance cars get their performance from the high-octane fuel, so it must be the best to use in their vehicles. Wrong...at least partly wrong. High-octane fuels resist detonation so engines can run higher compression ratios. Imagine two bottles of soda in the cup holders in your truck, one with a cork in it, and one with a normal screw-on top. Start driving down a potholed road and the pressure will drive the cork out of the bottle, leaving a big mess, but the cap will stay put, allowing you to open the soda whenever you want so you can spray the moron who put the other bottle in your truck in the first place. The bottle with the screw-on cap is like high-octane gasoline, not only can you contain more pressure, but you also have control over when that pressure is released.

The higher the compression, the higher the potential for power, but it's usually only worth 3 or 4 percent for each point the compression is raised. For example, a 300hp truck engine with 9.5:1 compression ratio would gain 9 to 12 hp if the compression ratio was increased to 10.5:1. That engine would definitely need a higher grade of fuel, but is it worth it? There are a lot of ways to gain 10 extra horsepower, and a lot of them are cheaper, especially since you pay for more expensive grades of fuel over the life of the vehicle. High-performance vehicles will definitely suffer if their octane needs are not met, but the opposite is not necessarily true. Unless your vehicle needs high-octane fuel, all you'll accomplish by topping off with premium is burning fuel that's costing you an extra 20 cents per gallon. How do you know if your truck needs premium fuel? We hate to say it, but your owner's manual would be a good place to start. If you've done anything to the engine to increase the compression ratio, like added a stroker crank, bolted on new heads, or added a super or turbocharger, then high-octane fuel could become a necessity. On newer vehicles, reprogramming the fuel and ignition timing curves could create a situation that would require high-octane fuels, but not necessarily.

So what happens if octane requirements aren't met? The air-fuel mixture can ignite at the wrong time, like the soda exploding in your truck. During pre-ignition, the combustion happens while the piston is in the middle of its compression stroke, creating unnecessary strain on the piston and the reciprocating assembly because the other pistons have to push against the force of a power stroke that happens too early. Not only does this rob your engine of power, it can seriously damage engine components; piston rings can break, and pistons can melt, putting a serious dent in your wallet. This early detonation is characterized by a pinging or knocking sound, so at least there's some warning that something bad is going on. Newer vehicles can often compensate for lower octane ratings, but performance will likely suffer. The knock sensor, part of a vehicle's on-board diagnostics, listens for the telltale sounds of pre-ignition and signals the ECM to retard the ignition and prevent the air/fuel mixture from pre-ignition. Older vehicles that have seen serious mileage or engines that are driven frequently without sufficient warm-up time might also need higher octane fuel to fight pre-ignition because of carbon deposits. Carbon deposits on the valves store combustion heat and can act like glow plugs. The same deposits can also increase the compression ratio by reducing the space inside the combustion chamber.

So, if you've been filling up with 92 octane to wring that last little bit of horsepower out of your truck, make sure it's really necessary. The odds are regular fuel will do just fine. Save your money and buy an intake system instead.

Alternative FuelsYou might have noticed that we said "nearly" every fuel comes from petroleum. The most notable exceptions to the petroleum standard are biodiesel and alcohol. Crude oil is made up of million-year-old plant and animal matter from prehistoric sea floors, which is why it's called a fossil fuel. Just think of biodiesel and alcohol as fossil fuels without the fossil part.

Plants that produce the oils we use for cooking can also be used for fuel, and it doesn't take them millions of years either. In fact, the diesel engine was designed to run on plant oil, but petroleum refining came into its own and biodiesel took a backseat. Recently, however, clean energy proponents have become vocal about biodiesel as a fossil fuel alternative.

Fresh from the deep fryer, straight vegetable oil (SVO) is not the best fuel, and engines need to be modified with glow plugs and filters to run properly, but biodiesel can be run in any diesel without any modification. Vegetable oils and animal fats are triglycerides, which means they contain glycerin. The biodiesel refining process leaves glycerin as a by-product and methyl esters remain as the fuel.

Another advantage of biodiesel is that it can be refined in your garage from used cooking oil that's either cheap or free, or clean oil that requires less processing. Unfortunately there is a small investment involved, and while the chemicals used in the reefing process are relatively safe, they still need to be handled carefully. Not to scare you away; if you are already on a first-name basis with the members of your local Hazmat crew you should be able to handle it. The advantages of biodiesel are being realized across the country and are really catching on in Europe. Most diesel sold in France contains 5 to 10 percent biodiesel, and Germany is stepping up to the plate with more than 1,500 stations selling biodiesel.

Ethanol is another renewable fuel that offers some of the same advantages of biodiesel. It's made from grain, typically corn, and it burns cleanly because it contains oxygen. In the Midwest, it's typical to find ethanol mixed with gasoline at a 1:9 ratio, which will run in any gasoline engine. In fact, every auto manufacturer that sells vehicles in the US covers ethanol use in their warranty. E85, which is 85 percent ethanol and 15 percent gasoline, is made to run in flexible fuel vehicles. The flexible part refers to the fact that engines can run on E85 or regular gasoline with out any modification between fill-ups, the fuel and ignition system recognizes which fuel is present and compensates. A bushel of corn can be distilled into about three gallons of ethanol, and the by-products are dried grain, which is used as a cattle feed, and CO2, which is collected for commercial and industrial use.

Alternative Fuel Advantages: Reduces dependence on foreign oil. Renewable, non-toxic, biodegradable. Acts as lubricant inside fuel system (biodiesel). Blends with diesel (biodiesel) or gasoline (ethanol). Reduces emissions. Protects against fuel-line freezing (ethanol). Exhaust smells like McDonalds (SVO).Drawbacks: Exhaust smell might pose a problem when the McAddict next to you in traffic thinks you're holding out on some French fries.